The study area of this research some 70 km southwest of Gedarif city, Gedarif State, in eastern Sudan. With a geological position, it is located within two major lithological associations, representing two different crustal entities: Saharan Meta-craton (SMC) in the west and the Arabian Nubian Shield (ANS) to the east. The main objective of the study is a petrological investigation of the mantle peridotites within Qala En Nahal-Umm Saqata area. The relatively large-scale exposed masses of mantle’s peridotite, include mainly the Utash mass and the Umm Saqata mass in the south and the Qala en Nahal mass and the Fau mass in the north of the area. Petrographically, they are mostly serpentinite. They have low-contents of Al2 O3, CaO, TiO 2, MgO, Na2O and K2O, all consistent with depleted mantle materials, and similar to the metamorphic peridotites. The analyzed serpentine minerals are mainly pseudomorphic serpentines with subordinate antigorite, which may suggest that the parent minerals were first retrogressed to form lizardite and chrysotile. Subsequently, progressive metamorphism has recrystallized these minerals into antigorite. The chromites from the study area have high Cr# (Cr# varies from 0.51 to 0.87), most probably representing the primary phase which is similar to chromian spinels in mantle-derived peridotites. The presence of podiform chromites in the studied serpentinites is e typical of supra-subduction ophiolites, with Cr# similar to those of forearc ophiolites and boninite-derived chromites. Qala En Nahal-Umm Saqata mantle peridotites were formed in a forearc setting, during the subduction initiation that developed as a result of southeastward-dipping subduction zone. They possibly represent ensimatic, thrusted material, after the collision of the Nubian-Arabian Shield with the older sialic continental Saharan Metacra-ton during the late Proterozoic, Pan-African tectono-thermal event. © 2021, Ore and Metals Publishing house. All rights reserved.